Ferrite-based compounds

The mechanical behavior of concrete should be viewed from the point of view of a composite material. A composite material is a three dimensional combination of at least two chemically and mechanically distinct materials with a definite interface separating the components. This multiphase material will have different properties from the original components. Concrete qualifies as such a multiphase material. Concrete is composed of hydrated cement paste (C-S-H, CH, aluminate, and ferrite-based compounds) and imhydrated cement, containing a network of a mixture of different materials. In dealing with cement paste behavior, basically it is considered that the paste consists of C-S-H and CH with a capillary system. The model of concrete is simplified by treating it as a matrix containing aggregate embedded in a matrix of cement paste. This model provides information on the mechanical properties of concrete. 

Cement binders are based on silicates, aluminates, aluminium silicates, aluminium ferrites of alkaline earth metals (mainly calcium). The hydration of these compounds or their mixtures with the formation of... 

These are obtained by dispersion of one or more solid fillers in a binder. The binder should be either inorganic (silica based ceramic) or organic (thermosetting or thermoplastic polymers) depending on the environmental conditions. Fillers are composed of ferrite described above with granulometry comprised between 12 and 100 pm and also of simple ferromagnetic compounds (Fe, Co, Ni) or complex alloys. 

A simple method of preparing single crystals is to melt the material and to crystallise it by slow cooling but practically all the ferrites dissociate at temperatures below their melting points, with loss of O2. To overcome this problem several techniques have been used which are based on the formation of a flux, a solution, or a volatile chemical compound to obtain ferrite single crystals. 

The proportion of metal added should be from about 0.01 to 5% by volume, based on the silica. It will be understood that this proportion is the total amount of modifying metal present but that more than a single metal can be used to attain this proportion. In such instances there can be found in the final supported catalysts of this invention, mixed oxides of the metals, compounds of two or more of the metals present with each other such as chromites, maganites, molybdates, tungstates, vanadates, cerates, stannates and ferrites. 

Ferrite Material based upon a form of iron oxide (FeO, Fe20g, or FegO ). The term typically implies magnetic behavior or response. The term can also be used to describe materials that show magnetic responses similar to those of known iron-containing compounds. 

A hard magnetic ferrite, also eaUed ferrite magnet, is a magnetic material based on iron oxide. The composition of the typical hard magnetic ferrite compounds is shown in Table 4.3-54. M t3tpe material is used most widely and BaO can be replaced by SrO. 

---